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Two months ago, a 61-year-old Ohio woman died after catching a
new strain of
swine flu. Her death was the first fatality linked to a
variant of influenza A virus H3N2 (H3N2v), which first appeared
in humans in 2011 and has infected more than 300 people this
year.

Like many individuals who caught H3N2v this summer, the woman who
died had contact
with pigs at a county fair, according to the Centers for
Disease Control and Prevention (CDC). The flu-risk at livestock
exhibitions might be especially high because the majority of
flu-positive pigs at county fairs don't show any outward signs of
illness, a new study suggests.

Researchers from Ohio State University tested 20 pigs at each of
53 county fairs during the summers of 2009, 2010 and 2011. They
found at least one pig tested positive for flu at 12 of the
fairs. Among those, 80 percent looked healthy. (The strains
identified in the study include H1N2 and H3N2 viruses, which have
been found in pigs since 1998.)

"This is an explanation of why people were becoming infected in
2012 — because a high percentage of infected pigs with no
clinical symptoms are exhibited at fairs," Richard Slemons, an
Ohio State professor of veterinary preventive medicine, said in a
statement. "There is potentially high exposure."

"If you bring 200-plus pigs together from multiple locations and
house them with new neighbors for a week in a new environment,
they are all bound to share pathogens," Bowman explained in a
statement. "But we were surprised to find as much flu as we did
subclinically, when pigs weren't showing any signs of illness."

In another study, the researchers compared virus isolates
collected from pigs at fairs during this past summer with
human-origin influenza A virus isolates recovered from people who
came down with the flu following exposure to pigs at an Ohio fair
in July 2012. They found more than a 99 percent similarity in the
genetic sequences of the virus isolates, confirming that the
illnesses were the same.

The researchers are not sure whether the infections are only
being transmitted in one direction, from pigs to humans.
According to the CDC, the virus can spread to humans in the same
way as human-to-human flus do, through droplets in the air. So if
one were to touch something, like a pig, with the virus and then
wipe your nose or mouth, there's a chance of transmission.

"It is possible that humans are infecting the pigs," Bowman said.
"The lineage of the H3N2 strains we see in pigs can be tracked
back to the human seasonal flu of the 1990s. Human-to-swine
transmission of influenza viruses has the potential to
significantly impact swine health."

Pigs' bodies are like melting pots for viruses. The more often
flu viruses hop between hog hosts, the better their chances are
of evolving into a strain that can affect humans, the researchers
said.

"Pigs can be infected with human-, avian- and swine-origin
influenza viruses, making it possible for these viruses to easily
swap their genetic material, which could allow for a new strain
to emerge," Bowman said. "The potential is there for newly
emerged strains to be the next pandemic we never saw coming."

The researchers said shortening the pig exhibition period,
vaccinating exhibition pigs and avoiding movement of hogs
from one fair to the next could help prevent flu transmission.
Additionally, the CDC recommends people with compromised immune
systems should avoid pig displays at fairs.

The study examining flu in Ohio county fair pigs from 2009-2011
was published in the journal Emerging Infectious Diseases. The
other study on the 2012 infections appears in the journal
Emerging Microbes & Infections.

And pigs are not alone in carrying the flu. Recent research
suggests cats
and dogs also get the flu more often than thought, and they
can get it from their owners.